I've never heard of putting it in an arena. I would hate to take a tumble there.
We spread our manure on the pastures in the late autumn and close them for the winter. In the spring and autumn we harrow. We keep one large pasture open for the winter and alternate each year. Maintaining a composting manure pile and recycling it onto your farm is lots of work but worth the effort. Thankfully I have a tractor. It takes some planning and consideration. We have a special concrete area that drains into a large tank (the run off or "soup" must be drained and is then sprayed on the pasture also). I can maintain the pile but I don't have the equipment to spread and spray so I hire a local farmer to do that. It is unlawful here to just put your "poop pile" anywhere. It can drain into the ground water or a water shed and it can really pollute the water. It sure can create the heat when its working well and I also use the good stuff for my garden.